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GENERAL ARTICLES

The Nonimmobilizer 1,2-Dichlorohexafluorocyclobutane Does Not Affect Thermoregulation in the Rat

Department of Anesthesia and Perioperative Care, University of California, San Francisco, California

Address correspondence to James M. Sonner, MD, Department of Anesthesia, 513 Parnassus Ave., Box 0464, University of California, San Francisco, CA 94143-0464. Address e-mail to sonnerj{at}anesthesia .ucsf.edu.

Inhaled and other anesthetics profoundly affect the central nervous system, causing amnesia, immobility in the face of noxious stimulation, and depression of thermoregulation. Nonimmobilizers, inhaled compounds whose lipophilicity suggests that they should be anesthetics, do not produce immobility, but they do cause amnesia. Their effects on thermoregulation were the subject of the present study. We gave eight rats isoflurane on one occasion and the nonimmobilizer 2N (1,2-dichlorolhexafluorocyclobutane) on another. We measured the effect of various concentrations of each compound on thermoregulation provoked by body cooling. The specific outcome was increased metabolism, as reflected in increased output of carbon dioxide. Isoflurane decreased the temperature threshold for such increases and the maximum response intensity, doing so in a concentration-dependent manner, whereas 2N had a minimal or no effect at any concentration up to 0.9 minimum alveolar concentration (estimated from its lipophilicity). Thus, 2N may be a useful tool for studies of the mechanisms mediating the thermoregulatory depression produced by anesthetics: 2N should not affect such a mechanism.

Implications: Unlike inhaled anesthetics, the nonimmobilizer 2N (1,2-dichlorohexafluorocyclobutane) minimally affects temperature regulation in rats. Thus, 2N may be useful in mechanistic studies of temperature regulation. Cellular and molecular sites that mediate the capacity of inhaled anesthetics to depress thermoregulation should be influenced by anesthetics but not by 2N.

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